Many predatory crabs don’t live in Antarctica for a simple reason: it’s too cold. But as the Earth warms, these clawed critters could invade pristine polar waters and threaten native species, scientists warn in an editorial.

The Southern Ocean “has traditionally been regarded as the most biologically isolated and invasion-resistant ocean,” the team writes in the Journal of Biogeography. Predatory crabs, known as “shell-breaking” crabs, probably haven’t lived in the area for millions of years. One reason is that many of these species can’t control the levels of magnesium ions in their bodies very well. In such a cold environment, high magnesium levels lead to paralysis and death.

But some crabs may find a way to survive. In February 2010, one of the co-authors discovered an adult female crab from the species Halicarcinus planatus on Deception Island, near the western Antarctic Peninsula. Normally, these crabs stick to warmer areas such as South America, New Zealand, and the Subantarctic. H. planatus could be among the first invaders because it’s better at magnesium regulation than other similar species.

King crabs also now live uncomfortably close to the peninsula and could pummel bottom-dwelling marine organisms if they spread, the team says. And the European green crab, which has already colonized other continents, could travel to Antarctica via South America or Africa. Tourist and fishing boats could carry invasive crabs on their hulls or in their ballast water.

The researchers aren’t panicking yet; after all, “[a] single crab at Deception Island does not constitute an invasion,” they write. But the island, which is a volcanic cone, offers a warm pocket of water where such crabs could thrive. Scientists need to keep a close watch on the area to find out how widespread the problem is, they say. — Roberta Kwok | 9 October 2014